The shooting occurred at around 8 a.m. ET at the New Castle County Courthouse in Wilmington, Del., when the gunman was stopped by Capitol Police at a security checkpoint inside the main lobby, Mayor Dennis Williams told NBC10 in Philadelphia. The court was not yet open.

Delaware State Police Sgt. Paul Shavack said that the two people wounded were Capitol Police officers. They were transported to Christiana Hospital in Newark, Del., with non-life threatening injuries.

Shavack said the suspect exchanged gunfire with officers in the lobby. It was not immediately known whether the suspect was killed by police or died of a self-inflicted wound.

Police said they have preliminary identification of the gunman, who was in his late 20s to early 30s, but would not yet release that information.

Shavack said investigators and search teams were canvassing the 12-story courthouse building as a precaution to protect those still inside, but they believed the area was secure.

“We believe that this is a lone gunman but we continue to operate under procedure,” Shavack told reporters outside the courthouse Monday.

Defense attorney Brian Chapman told NBCPhiladelphia.com that the building’s security personnel make it very hard to breach security.

"There are at least four or five rows of metal detectors when you go in, you put your belongings through, then you have to walk through the metal detectors,” Chapman said. “Then there are usually eight to 10 police with wands checking everyone and after that you still have to walk by a desk where capitol police sit."

Dozens of police cars, ambulances and fire trucks were on the scene, and the streets were cordoned off for several blocks around the courthouse, DelawareOnline.com reported.

Five elementary schools and one high school in the area were on lockdown Monday morning.